There are many useful chemical compounds which, given their limited occurrence in nature, are manufactured through chemical processes in which oppositely charged ions from one compound are exchanged for those of another. Because such processes typically involve a large number of steps to reach the final product, requiring formation of many intermediate chemicals and also using a large amount of energy, there is a need for simplification of these processes and the reduction of energy consumption for their manufacture.
Synthesis of such useful chemical compounds from chemicals containing the constituent elements of these compounds is an ongoing goal of research and development in the chemical industry. Known synthesis processes that have proven successful have been more direct and less energy intensive. One example is the Solvay process for manufacture of sodium carbonate from sodium chloride (common salt) and calcium carbonate (Lime Stone) using ammonia. The overall chemical equation for the Solvay Process can be written as:CaCO3+2NaCl→Na2CO3+CaCl2   (Equation 1)
However, in order to reach the end products, the Solvay process involves many intermediate steps, and is centered about a large hollow tower. At the bottom of the tower, calcium carbonate (limestone) is heated to release carbon dioxide:CaCO3→CaO+CO2 
At the top of the tower, a concentrated solution of sodium chloride and ammonia enter the tower. As the carbon dioxide bubbles up through it, sodium bicarbonate is precipitated according to the following equation:NaCl+NH3+CO2+H2O→NaHCO3+NH4Cl
The sodium bicarbonate is then converted to sodium carbonate by heating it, releasing water and carbon dioxide:2NaHCO3→Na2CO3+H2O+CO2 
Meanwhile, the ammonia is regenerated from the ammonium chloride byproduct by treating it with the lime (calcium hydroxide) left over from carbon dioxide generation:CaO+H2O→Ca(OH)2 Ca(OH)2+2NH4Cl→CaCl2+2NH3+2H2O
Looking at Equation 1 above and comparing it to the many steps needed to accomplish the Solvay Process, it is apparent that it would be beneficial if the constituent ions of calcium carbonate and sodium chloride can be independently isolated and recombined in a single step.
Another case in point is production of sodium hydroxide (NaOH) and hydrochloric acid (HCl) from common salt and water. The overall chemical equation for this process is:NaCl+H2O→NaOH+HCl   (Equation 2)
However, this process involves the electrolysis of salt to generate sodium hydroxide and chlorine and hydrogen gases at great expenditure of electric energy followed by reaction of hydrogen and chlorine gases. However, if sodium and chlorine ions can be independently isolated, as well as the constituent ions of water, then by mixing oppositely charged ions of the two input chemicals, the final products of sodium hydroxide and hydrochloric acid can be more quickly and easily generated.
The chemical equations above all adhere to the principal of electro-neutrality, which means that, in uncharged electrolytic solutions, the concentrations of all ionic species are such that the solution as a whole remains electrically neutral. That is, if one removes a certain amount of positively charged ions from an uncharged electrolyte solution, the remaining negatively charged solution cannot regain its electric neutrality until the same amount of negative charges are also removed, or until the balance of positively charged ions are returned to the solution. Due to the great attractive forces generated by positive and negative charge separation, the synthesis processes for various compounds have been based traditionally on phase shift techniques, such as precipitation, evaporation or electrolytic techniques in which electric charge balance are constantly maintained.
The present invention has the goal of synthesizing new chemical compounds that traditionally have been hard to construct, by exchanging oppositely charged ions from one chemical compound for those of another. The invention also provides an innovative apparatus and method for desalination of water by selective removal and depletion of ions.
Conventional desalination processes presently being used include distillation, ion exchange, reverse osmosis, electro-dialysis and filtering. Distillation is probably the oldest method of water purification. Water is first heated to boiling, and the water vapor rises to a condenser where cooling water lowers the temperature so the vapor is condensed, collected and stored. Most contaminants remain behind in the liquid phase vessel. However, even modern distillation techniques such as multi-stage flash distillation and multi-effect distillation can be expensive, as they require large amounts of energy to evaporate the water and condense the fluid. Also, organics with low boiling points cannot be removed efficiently from the distillate, and can become concentrated in the product water.
Reverse Osmosis (RO) in recent years has been the preferred choice for new desalination facilities, producing potable water by blocking the passage of ions through the membranes used. However, the process requires expensive membranes that must be meticulously maintained and replaced at regular intervals, and high pressure and energy to push saline water through the very tight membranes.
Electro-dialysis (ED) is a combination of electrolysis and ion exchange, resulting in a process which effectively deionizes water while the ion exchange resins are continuously regenerated by the electric current in the unit. This electrochemical regeneration replaces the chemical regeneration of conventional ion exchange systems. In this method, two electrodes are positioned on the two sides of a stack of anion and cation exchange membranes, typically referred to as an electrolysis cell. The spacings between these membranes define compartments through which water can flow. Saline water is made to flow through all these compartments while an electric field is established between the two electrodes. The outlets from every other compartment are connected together. The stack is setup such that a cation exchange membrane faces the cathode (negative electrode) and an anion exchange membrane faces the anode (positive electrode). Movement of cations towards the cathode and anions towards the anode causes the depletion of both ions from every other compartment referred to as dilute compartments and their concentration in the compartments between the dilute compartments called concentrated compartments.
As with RO, electrodialysis systems require feed pre-treatment to remove species that coat, precipitate onto, or otherwise “foul” the surface of the ion exchange membranes. However, electrodialysis reversal can minimize scaling by periodically reversing the polarity of the electrodes and/or the flows of the diluent and concentrate streams. When polarity of the applied potential between the two electrodes is reversed, the dilute compartments become concentrated compartments and vice versa. This reversal process is used to clean and rejuvenate the membranes.
A great deal of innovative work has recently been done on ED technology. For example, published U.S. Patent App. No. 2011/0180477 to Ganzi et al discloses use of a pair of electrodialysis devices containing monoselective membranes to partially desalinate the seawater being treated. The dilute stream from both devices are sent to an ion exchange softener where calcium and other scaling ions are removed or reduced in concentration, and the effluent from the softener is sent to an electrodeionization device to produce final water product. Despite improvements, ED technology still suffers from a number of shortcomings, such as high energy consumption and the need to pre-purify the incoming water, such as with reverse osmosis.
Capacitive deionization (CDI) is an emerging electrochemical water treatment technology that uses electrophoretic driving forces to achieve desalination. While CDI, like electrodialysis, drives ions to the electrodes, CDI does not involve membranes. It is therefore a low pressure process of deionization that has the possibility of directly competing with reverse osmosis or distillation as a means of delivering water free of ions at reduced cost and operating expense.
CDI works by sequestering ions or other charged species in the electrical double layer of ultracapacitors. During CDI, ions are adsorbed or captured onto the surface of porous electrodes by applying a low voltage (1.0-1.7 VDC) electric field. The negative electrodes attract positively charged ions such as sodium, calcium, and magnesium; simultaneously, the positive electrodes attract negatively charged ions such as chloride, nitrate and sulfate. Unlike ion exchange processes, no additional chemicals are required for regeneration of the electrosorbent in this system. Eliminating the electric field allows ions to desorb from the surface of the electrodes and regenerates the electrodes. The amount of charge that can be collected is determined by the surface area available on the electrodes.
There are a variety of CDI electrode materials and configurations to enhance performance. Optimized carbon aerogel is an ideal electrode material because of its high electrical conductivity, high specific surface area, and controllable pore size distribution. In the charging cycles of these capacitors, equal amounts of positively and negatively charged ions are removed from the base electrolytic solutions (saline water) and are attracted to the capacitor plates. Through many cycles of passage of a given volume of electrolyte solution between the capacitor plates, reduction in ion content is achieved.
CDI technology has received considerable attention due to its potential for lower energy consumption, and has been under continuous development since the early 1970's. Even so, due to limitations in the amount of ions removed, and the time it takes to remove these ions, capacitive deionization technology has been limited to low salinity waters and deionization applications. Typical among earlier developments in this field are U.S. Pat. No. 5,425,858 to Farmer and U.S. Pat. No. 5,789,338 to Kaschmitter. These patents exemplify the use of flow-through capacitors (meaning that saline water flows through the capacitor and in between capacitor plates) and developments in carbonaceous high capacitance capacitor plate materials, respectively.
Most current CDI technologies use capacitor plate arrangements that follow various forms of parallel plate capacitors, as exemplified by U.S. Pat. No. 5,620,597 to Andelman. Further developments of higher electrical capacitance and lower electrical resistance capacitor plate materials are exemplified by U.S. Pat. No. 5,626,977 to Mayer et al. and U.S. Pat. No. 7,505,250 to Cho et al. There have also been attempts at improving the efficiency of the charging and discharging cycles by specific electric circuitry as exemplified by U.S. Pat. No. 7,138,042 to Tran et al.
While known desalination methods and devices may be useful for their intended purposes, there currently is no device or method for synthesizing new and useful chemical compounds from the byproducts of desalination. It would thus be beneficial to provide a desalination device that can provide a means for creating new chemical compounds from other chemical compounds containing their constituent elements. It would also be beneficial to simplify the manufacture of various chemical substances and to reduce the energy consumption for their manufacture. There is also a need for further improvement of ion separation technology by substantially increasing the amount of ions removed in any given time span.